1. Understanding Populations
Chapter 8
Understanding Populations

2. 8-1: How Populations Change Size
Describe the three main properties of a population. (slide 3 & 4)
Describe exponential population growth. (slide 6, 7, 11, 12)
Describe how the reproductive behavior of individuals can affect the growth rate of their population. (slide 6 & 7)
Explain how population sizes in nature are regulated. (slide 8)

3. What is a population?
All the members of the same species living in the same place at the same time.
“reproductive group” or “gene pool”
Population refers to the group in general and to the size of the group
Daisies in Ohio, not in Maryland
Bass in a lake in Iowa
Properties of populations:
Size
Density
Dispersion

4. Size Density Dispersion Number of individuals in the population
250,000 people in Kalamazoo County (2010 census)
Density
Individuals per unit of area or volume
75 deer per square mile
Dispersion
Distribution or arrangement
Even – pine trees in rows in a forest; corn fields
Clumped – zebras in the savanna; deer herds
Random- dandelions in a field; lizards in the desert

5. Population Growth Growth rate is calculated using
change in = births – deaths
population size
*Also included would be immigrants (in) to the area and emigrants (out) from the area
*Growth rate can be positive or negative numbers; with negative numbers equaling a decrease in population size

6. Growth Curves Earlier maturity Larger numbers of eggs
Biotic potential = fastest rate at which a population can grow. This is also called fercundity (max number of offspring that could be produced vs fertility which is number actually produced).
Reproductive potential = max. number that a population can produce.
Earlier maturity
Larger numbers of eggs
Shorter generation time
Survival rate

7. Sea turtle lay >2000 eggs, they don’t all survive
A pair of elephants could produce 19 million descendants in 750 years….but have one at a time, gestate 20+ months, nurse 4+ years, 15 when mature, raise 1 at a time; even if live to be 100 – only have a couple kids
Bacteria and insects have very short generation times.
Average generation time for humans is 20 years

8. Limits to population growth
Resources are never unlimited or constant; they are either used up or they change.
A limited resource is something the species needs and consumes at the same rate its produced.
Leads to competition
Carrying capacity = theoretical limit to populations size in a given ecosystem.
Rabbits in Australia
Islands make good studies because of boundaries
Regulation
Density dependent – rate of death is worse when individuals are closely packed (infection in pine trees)
Density independent – rate of death is not dependent on numbers of individuals in the area; storms, crops freezing , etc.

9. 8-2: How Species Interact with Each Other
Explain the difference between niche and habitat. (slide 17-19)
Give examples of parts of a niche. (slide 17-19)
Describe the five major types of interactions between species. (slide 14 & 15)
Explain the difference between parasitism and predation. (slide 14)
Explain how symbiotic relationships may evolve.

10. 8.2: Population Dynamics
Population – group of similar individuals that are in the same place, at the same time and comprise a gene pool
Species – organisms that are similar enough to interbreed in nature and produce viable offspring.
Breed, variety, strain, subspecies, etc.
“dynamic” means in constant motion, always changing, not static.

11. Births increase population
Deaths decrease population
If births = deaths then population is steady, called “replacement rate”
If growth is exponential, then population increases rapidly…. Parents have 2 kids (4) and they each have 2 kids (8), and they have 2 kids (16)….. The sum of population would go like this 2,4,8,16,32….

12. Population Growth patterns
Logistic – steady (“S”)
Exponential – increasing rapidly (“J”)
In a new situation, populations have the potential to increase exponentially, but natural forces like food/resources, predators and space will eventually create a stable level when the population reaches “Carrying Capacity”

14. Symbiosis
In addition to enough food, water, oxygen, sun, space, mates and other resources – individuals have interactions with other species that impact their survival and reproductive success.
Competition (bugs and food)
Can be direct or indirect
NOT an example of symbiosis!
Predator – prey (rabbit – lynx)
Commensalism (bromeliads like orchids)
Mutualism (acacia/ants, pollinators/flowering plants, intestinal bacteria)
Parasitism (mosquito, lice, leech, tapeworm)

17. Resource Partitioning
In order to decrease competition some resources are allocated or partitioned to specific species
Common examples include birds that specifically live in the upper branches, lower branches, or interior of the tree so that one tree can house 3 species in their own separate zones

19. Niche
An organism’s unique role within an ecosystem is it’s NICHE; FUNCTION or job… “grazer”, “pollinator”, etc
Physical space +
Environmental factors +
Interactions
Realized Niche vs Fundamental Niche
Where you actually are vs. anywhere you could be successful
HABITAT= WHERE you live

20. Humans
The human population is also subject to all of the conditions studied in ecology
Resource availability (coal, Al, transportation, Rx)
Material resources, goods and infrastructure including services
Water, air, food
Space
Waste
Pollution Disease/ immunity
Genetic impacts “Creativity”
Carrying capacity is hard to calculate due to the number of variables.